apply-discount-function

A small Python module that calculates the final price after applying a percentage discount. It exposes a single reusable function, apply_discount, which validates its inputs and returns either the discounted price or a human-readable error message.

Contents

File	Description
main.py	Defines the apply_discount function.
LICENSE	CC0 1.0 Universal public domain dedication.
.gitignore	Standard Python ignore rules for version control.

Getting started

1. Make sure you have Python 3 installed.

2. Import and call the function from your own code, or test it directly:

   python -c "from main import apply_discount; print(apply_discount(100, 20))"

How it works

The apply_discount function takes a price and a discount (both expected to be numbers) and returns the final price after the discount is applied.

def apply_discount(price, discount):

    if type(price) not in [int, float]:
        return "The price should be a number"

    if type(discount) not in [int, float]:
        return "The discount should be a number"

    if price <= 0:
        return "The price should be greater than 0"

    if discount < 0 or discount > 100:
        return "The discount should be between 0 and 100"

    discount_amount = price * (discount / 100)
    final_price = price - discount_amount

    return final_price

Validation rules

Before computing anything, the function checks the inputs and returns an error string when a rule is violated:

• price must be an int or float, otherwise "The price should be a number".
• discount must be an int or float, otherwise "The discount should be a number".
• price must be greater than 0, otherwise "The price should be greater than 0".
• discount must be between 0 and 100 inclusive, otherwise "The discount should be between 0 and 100".

When all checks pass, it computes discount_amount = price * (discount / 100) and returns final_price = price - discount_amount.

Example usage

from main import apply_discount

print(apply_discount(100, 20))        # 80.0
print(apply_discount(50, 10))         # 45.0
print(apply_discount(100, 0))         # 100.0
print(apply_discount(100, 100))       # 0.0
print(apply_discount("100", 20))      # The price should be a number
print(apply_discount(100, 150))       # The discount should be between 0 and 100

Note: the module itself only defines the function — it has no top-level print calls, so running python main.py produces no output. Import it as shown above to use it.

Key concepts

• Define a function with parameters and a return value.
• Validate inputs with guard clauses that return early on bad data.
• Use type() and a list membership check (in [...]) to accept multiple numeric types.
• Compute a percentage-based discount and return a clean result.

License

Released under CC0 1.0, placing the work in the public domain.